1. Field of the Invention
The present invention generally relates to the testing of battery designs, and more particularly relates to tests which determine the full or residual charge capacity of a battery. The present invention is most relevant to those who seek a relatively rapid method to ascertain the total electrical energy of a new, modified or previously untested battery design. The present invention has some relation to the art of battery charging wherein the charge accepted by a battery is maximized by a relatively sophisticated charging regimen.
2. Background Art
One approach to battery capacity testing has been described by Doyle et al. in the article, “A Quick Method of Measuring the Capacity Versus Discharge Rate for a Dual Lithium-ion Insertion Cell Undergoing Cycling.” The Doyle article focuses on finding the battery capacity as a function of discharge rate. It teaches successive discharges of a battery to a cutoff potential starting with the highest discharge rate followed by discharges at ever decreasing rates. The capacity obtained at a given discharge rate is assumed to correspond to cumulative battery capacity discharged up to that time. Each discharge is preceded by a brief relaxation period but is never preceded by a charging step. Doyle indicates (page 213, top of right column) that this method is relatively insensitive to length of relaxation periods.
In U.S. Pat. No. 5,381,350 to Fiorina et al., the backup time of a battery is estimated in an iterative manner by discharging the battery during successive estimated time intervals. During each of these intervals, an estimated discharge current in terms of actual discharge power, an estimated voltage, and an estimated state of charge are computed in accordance with a mathematical model equivalent to the battery. The backup time for the battery is equal to the sum of the estimated time intervals necessary for the estimated voltage to reach a preset threshold.
U.S. Pat. No. 6,232,750 B1 to Podrazhansky et al. shows a method to charge batteries wherein size of charge pulses, discharge pulses and relaxation periods depend on feedback obtained during the battery charging process. The charge and discharge pulses can vary in current, voltage, duration, frequency and number of applications. Relaxation periods can be varied by frequency or duration. Podrazhansky also uses short, isolated AC pulses to create a mixing of electrolytic reagents near the battery plates. Other isolated AC pulses, of a different frequency, are used in measuring the capacitance, condition or state of charge of the battery.
U.S. Pat. No. 5,307,000 to Podrazhansky et al. shows a method for rapidly thawing and charging a battery. This Podrazhansky patent uses variable charge pulses, discharge pulses and waiting periods whose values depend on certain parameters occurring as the battery thaws and becomes charged. The duration, number, and magnitude of the charging pulses are controlled so as to maintain the electrolyte's temperature within an optimal range. The duration and number of the discharging pulses is selected to maximize the availability of ions, obtain a desired crystal size of material deposits on the plates and minimize the formation of sharp edges on the crystals. The duration of the waiting periods is varied so as to maximize the availability of ions.
U.S. Pat. No. 6,198,251 B1 to Landon shows battery charging wherein charging current is turned off and on periodically to allow gases formed during charging to recombine with the battery's electrolytic solution. Landon also teaches applying a short discharge pulse during the period of recombination to “clean up” newly deposited material at the battery plates. U.S. patent to Ayers et al. has a battery recharge method which first introduces stepped charge current to restore a majority of energy to a deeply discharged battery. Then low frequency charge and discharge currents interspersed with relaxation periods are used to complete restoration of energy to the battery. U.S. Pat. No. 6,137,804 to Oglesbee et al. discusses the calculation of relaxation periods for the charging process of a lithium-ion battery and suggests relaxation periods that are 30 to 300 seconds long. An article at Journal of Power Sources 102 (2001) 302-309 by Li et “The Effects of Pulse Charging on Cycling Characteristics of Commercial Lithium-ion Batteries,” discusses charging of lithium-ion batteries wherein relaxation periods are interposed between charging periods.